JP5810964B2 - Molding method of resin molded products - Google Patents

Description

  The present invention relates to a method for molding a resin molded product by injection molding a resin molded product having ribs.

In recent years, in order to reduce carbon dioxide (CO ₂ ) emitted from vehicles such as automobiles, improvement in fuel efficiency has been demanded, and vehicle weight reduction is essential. As a part of such weight reduction of the vehicle, a technique for reducing the weight of the interior resin parts such as automobiles by reducing the thickness has been proposed so far, but it becomes difficult to secure rigidity if the product is reduced in thickness.

  Therefore, it is known to apply injection foam molding as a method for ensuring rigidity while reducing the weight (see Patent Document 1). In this injection foaming molding, for example, a pair of molds that can be opened and closed is applied, and in a state in which both molds are assembled, a molten resin material to which a foaming agent is added is injected into the mold, and then one side is molded. This is a method in which foaming is performed by opening a predetermined amount of the molds and separating them from each other (hereinafter referred to as “core back”). By foaming the resin material, the thickness of the resin molded product (foamed molded product) is increased, so that rigidity can be ensured as compared with the case where the resin molded product is thinned and reduced in weight.

  On the other hand, in normal injection molding in which injection molding is performed without adding a foaming agent to a resin material, ribs are provided to ensure the rigidity of the resin molded product. However, when the rib is provided, there is a problem that a dent (sink) is generated in the vicinity of the rib due to contraction during molding of the resin depending on the basic thickness of the resin molded product and the dimension of the base width of the rib. On the other hand, the above-described injection foam molding has an advantage that the above-mentioned sink does not occur because the rib base part is also foamed by the core back operation.

JP 2005-271499 A

  However, the resin molded product has a box shape in which the standing wall portion is erected from the bottom surface portion, and the bottom surface portion is positioned perpendicular to the core back direction at the time of injection foam molding by the core back, and the standing wall portion is When positioned parallel to the core back direction, the standing wall portion does not increase in thickness even by the core back. Therefore, when the rib is provided on the standing wall portion, the resin material hardly foams even at the base portion of the rib, so that there is a problem that a sink mark is generated in the vicinity of the rib (see sink mark 7 in FIG. 6B). ).

  Further, in the injection foam molding, the pressure is released at the moment when the molten resin material is injected into the cavity from the gate of the mold, and the resin material starts to foam. Therefore, the molten resin material injected into the mold flows in the mold while foaming. At this time, silver-white streaks (swirl marks) caused by the bursting of bubbles are formed on the surface of the resin molded product. Occur. Further, when the resin material entrains air in the flow process of the molten resin material, a depression is generated on the surface of the resin molded product, resulting in appearance defects.

  An object of the present invention is to provide a method for molding a resin molded product that can prevent the occurrence of sink marks in the vicinity of the ribs of the resin molded product.

The present invention applies a molding die composed of a fixed die and a movable die movable relative to the fixed die, and assembles these two dies so that the gate communicates with the gate between the fixed die and the movable die. The cavity is filled with a resin material to which a foaming agent is added from the gate in a molten state, and then the movable mold is core-backed by a predetermined amount with respect to the fixed mold, so that at least the core back has a thickness. From the vertical molding part in the region located substantially perpendicular to the core back direction, which has a large increase in thickness, and from the vertical molding part in the region located substantially parallel to the core back direction, where the increase in thickness is small due to the core back. Thickness is also provided by a parallel molding portion standing upright in a substantially perpendicular direction and a core back provided along a wall surface of the parallel molding portion at a predetermined distance from the gate of the parallel molding portion. Increase in the small core back direction and a reinforcing rib substantially parallel, in the molding method of a resin molded article for molding the resin molded article having, as the gate communicating with the cavity, provided along the parallel shaped portion the thickness of the upstream portion in the parallel shaped portion between said ribs and thinner than the thickness of the downstream portion in the parallel shaped portion extending in a direction opposite to said gate from said rib, said cavity from the gate About the resin material in a molten state injected into the thickness of the thin upstream portion, the foaming is suppressed by suppressing a rapid drop in injection pressure, and the thickness extends from the rib in the opposite direction to the gate. In the region of the thick downstream side, the pressure reduction rate of the injection pressure is increased to promote foaming.

  According to the present invention, in the molten resin material injected from the gate into the cavity, foaming is suppressed in the region corresponding to the upstream portion from the gate to the rib of the resin molded product, and the rib from the rib of the resin molded product to the gate. Since the foaming is promoted in the region corresponding to the downstream portion extending in the opposite direction, the occurrence of sink marks in the vicinity of the rib of the resin molded product can be prevented by the foaming of the resin material at the rib base portion.

The operation | movement figure explaining the molding method of the foaming molded product to which one Embodiment in the molding method of the resin molded product which concerns on this invention was applied. Sectional drawing which shows the shaping | molding die of the mold clamping process of FIG. Sectional drawing which shows the shaping | molding die of the injection process of FIG. Sectional drawing which shows the shaping | molding die of the core back process of FIG. 1, and a cooling process. The perspective view which shows the foaming molded article of FIG. FIG. 6 is a view taken in the direction of arrow VI in FIG. 5, (A) shows the case of the present embodiment, and (B) shows the conventional case. The chart which shows the specification of the injection molding machine of FIG. The chart which shows the shape of the foaming molded product of FIG. 5 by comparing with an Example and a prior art example. The chart which shows the molding conditions in a core back process. The figure which shows the external appearance of a foaming molded product, and the generation | occurrence | production state of sink marks by comparing an Example and a conventional example.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is an operation diagram illustrating a method for molding a foam molded product to which an embodiment of the method for molding a resin molded product according to the present invention is applied. FIG. 2 is a cross-sectional view showing a mold in the mold clamping step of FIG.

  As shown in FIGS. 1A and 2, the molding die 10 of the present embodiment is moved with respect to a stationary die 11 to which a molten resin material 1 is supplied from an injection molding machine 13 and the stationary die 11. The movable mold 12 is configured to be attached.

  The fixed mold 11 is configured as a block body having a concave shape as a whole, and is formed, for example, in a shape in which a concave portion 11A is provided at the center position. The movable die 12 is configured as a block body having a convex cross section having a convex portion 12A having a convex shape that can be fitted into the concave portion 11A of the fixed die 11. The moving amount of the movable die 12 with respect to the fixed die 11 is configured to be adjustable.

  A cavity 14 for injection foam molding is formed at the joining position of the fixed mold 11 and the movable mold 12, that is, between the concave portion 11A of the fixed mold 11 and the convex portion 12A of the movable mold 12. In the movable mold 12, a gate 15 and a cold runner 16 are formed successively in the cavity 14, and in the fixed mold 11, a hot runner 17 is formed continuous with the cold runner 16. An injection molding machine 13 communicates with and is connected to the hot runner 17. A valve pin (not shown) for controlling the flow of the molten resin material 1 is installed at a position where the hot runner 17 is connected to the cold runner 16.

  The injection molding machine 13 adds and mixes a chemical foaming agent such as sodium hydrocarbon to a thermoplastic resin material such as polypropylene and heats it to a molten state. The molten resin material 1 to which the foaming agent has been added is injected from the injection molding machine 13 through the hot runner 17, the cold runner 16 and the gate 15 into the cavity 14 and filled in the cavity 14. The resin material 1 filled in the cavity 14 is foam-molded with a foaming agent as will be described later to become a foam-molded product 2 as a resin-molded product.

  The foam molding process of the foam molded product 2 will be described mainly with reference to FIG. First, the mold 10 including the fixed mold 11 and the movable mold 12 is clamped (FIGS. 1A and 2). Next, in this state, the resin material 1 containing the foaming agent is injected and filled into the cavity 14 of the mold 10 from the injection molding machine 13 (FIGS. 1B and 3). Thereafter, the movable mold 12 is separated from the fixed mold 11 by a predetermined amount in the direction of the arrow α (core back), the resin material 1 in the cavity 14 is foamed with a foaming agent, and cooled after the completion of the core back (FIG. 1). (C) and FIG. 4). After completion of the cooling, the movable mold 12 is further separated from the fixed mold 11 (FIG. 1D), and the foamed molded product 2 molded in the cavity 14 is taken out (FIG. 1E).

  By the way, as shown in FIG. 5, the foam molded product 2 molded by the injection foam molding process as described above includes a door trim board of a four-wheeled vehicle in which a standing wall portion 4 is erected from the periphery of the bottom surface portion 3. It is a box-shaped molded body used for a back door trim. As shown in FIGS. 2, 4, and 5, the gate 15 of the molding die 10 is provided continuously to the standing wall portion 4 of the foam molded product 2.

  Further, as shown in FIGS. 1C and 4, the standing wall portion 4 of the foam molded product 2 has a bottom surface portion in parallel with a direction away from the fixed die 11 (arrow α) of the movable die 12 in the core back. It is erected from 3. Therefore, since this standing wall part 4 becomes a part with little increase in thickness even by the core back, as shown in FIG. 5, in order to ensure the rigidity of this standing wall part 4, The rib 5 is provided at a position away from the gate 15 by a predetermined distance. 2 to 4 is a rib recess provided in the movable mold 12 as a part of the cavity 14 in order to form the rib 5 on the standing wall 4.

  However, as described above, since the standing wall portion 4 is a portion where the increase in thickness due to the core back is small, the resin material 1 is difficult to foam, particularly at the root portion of the rib 5, and as a result, as shown in FIG. Thus, in the conventional standing wall portion 6 having the same thickness, sink marks (dents) 7 are generated in the vicinity of the ribs 5. In the present embodiment, in particular, in order to prevent the occurrence of sink marks 7, the standing wall portion 4 of the foam molded product 2 has an upstream portion 4A from the gate 15 to the rib 5 as shown in FIG. The thickness tA (not including the rib 5) is provided smaller than the thickness tB of the downstream portion 4B (portion including the rib 5) extending from the rib 5 in the direction opposite to the gate 15 (tA <tB). .

  As described above, the thickness tA of the upstream portion 4A in the standing wall 4 is set to be thinner than the thickness tB of the downstream portion 4B, so that the inside of the cavity 14 can be obtained at the time of injection in FIGS. Then, in the region corresponding to the upstream portion 4A of the standing wall 4 (FIG. 6A), the rapid decrease in pressure around the gate 15 is suppressed, so that the melt injected into the cavity 14 from the gate 15 In the resin material 1 in the state, foaming is suppressed in a region corresponding to the upstream portion 4A of the standing wall portion 4, and the occurrence of swirl marks and avatars peculiar to injection foam molding is reduced. Further, at the time of injection in FIG. 1B and FIG. 3, the decompression speed increases in the region corresponding to the downstream portion 4B of the standing wall 4 in the cavity 14, so that the molten resin material 1 in the cavity 14 In the region corresponding to the downstream portion 4B, foaming is promoted. Particularly, the foaming of the resin material 1 is promoted at the root portion of the rib 5, and the sink wall 7 (FIG. 6 (B )) Is prevented.

  Specifically, the difference between the thickness tA of the upstream portion 4A and the thickness tB of the downstream portion 4B of the standing wall 4 in the foam molded product 2 is preferably set to 0.5 mm or more. Further, the thickness tA of the upstream portion 4A of the standing wall 4 is set to be equal to or larger than the root width tC of the root of the rib 5 (tA ≧ tC). Furthermore, in order to more reliably suppress foaming of the resin material 1 in a region corresponding to the upstream portion 4A of the standing wall portion 4 in the cavity 14, the thickness tA of the upstream portion 4A of the standing wall portion 4 is 1. It is desirable that it is 5 mm or less.

Next, an example to which the present embodiment is applied will be described in comparison with a conventional example to which a conventional technique is applied.
In the examples and the conventional example, the resin material is polypropylene to which a chemical foaming agent is added, and the same model having the specifications shown in FIG. 7 is used for the injection molding machine.

  In addition, as the molds of the example and the conventional example, a mold having a cavity in which the foamed molded product to be molded has a shape shown in FIG. 8 is used. That is, the thickness tA of the upstream portion of the standing wall portion in the foamed molded product is tA = 1.2 mm in the embodiment and tA = 2.0 mm in the conventional example, and the thickness tB of the downstream portion of the standing wall portion. In the example and the conventional example, tB = 2.0 mm, and the root width tC of the rib is tC = 1.2 mm in both the example and the conventional example.

  In the injection foam molding process, in both the example and the conventional example, after completion of the mold clamping shown in FIG. 2, as shown in FIG. 3, the resin material added with the chemical foaming agent is injected into the cavity of the molding die and filled. Then, after the completion of filling, the core back was executed under the conditions shown in FIG. 9, and after cooling, the foamed molded product was taken out. The core back delay time in FIG. 9 is a waiting time from the completion of injection to the start of core back, and is set to execute the core back after the skin layer is formed on the surface of the resin material injected into the cavity. It has been done.

  FIG. 10 shows the appearance and the state of sink marks of the molded foam product that has been molded and taken out. In the foamed molded product of the conventional example, a lot of swirl marks and avatars are generated particularly in the upstream portion 6A (portion from the gate 15 to the rib 5) in the standing wall portion 6 shown in FIG. The sink marks 7 are generated in the vicinity of the rib 5 in the portion 6B (the portion extending from the rib 5 to the side opposite to the gate 15). In contrast, in the foamed molded product of the embodiment, swirl marks and avatars generated in the upstream portion 4A of the standing wall portion 4 shown in FIG. 6A are reduced, and further, the downstream portion of the standing wall portion 4 is reduced. There was no sink mark 7 near the rib 5 in 4B.

With the configuration as described above, the present embodiment has the following effects.
When the resin material 1 to which a foaming agent is added is filled in the cavity 14 of the mold 10 in a molten state, and the foamed molded product 2 in which the standing wall portion 4 is erected from the bottom surface portion 3 is molded, The communicating gate 15 is continuous with the standing wall portion 4 of the foamed molded product 2, and this standing wall portion 4 includes a rib 5 at a predetermined distance from the gate 15 and an upstream portion from the gate 15 to the rib 5. The thickness tA of 4A is provided thinner than the thickness tB of the downstream portion 4B extending from the rib 5 to the opposite side of the gate 15 (tA <tB).

  Accordingly, in the molten resin material 1 injected from the gate 15 into the cavity 14, foaming is suppressed in the region corresponding to the upstream portion 4 </ b> A of the standing wall portion 4 of the foam molded product 2, and the downstream of the standing wall portion 4. Foaming can be promoted in the region corresponding to the side portion 4B. As a result, the foaming of the resin material 1 at the root portion of the rib 5 can prevent the occurrence of sink marks 7 in the vicinity of the rib 5 in the standing wall portion 4 of the foam molded product 2, and the standing wall portion 4 of the foam molded product 2. The occurrence of swirl marks and avatars in the upstream portion 4A can be suppressed.

  Although the embodiment has been described above, the present invention is not limited to the specific configuration of the embodiment as described above, and various modifications can be made without departing from the gist of the present invention. For example, even when a resin molded product having ribs is injection molded without a core back process using a resin material to which a foaming agent is added (that is, when the core back process is omitted in the molding method shown in FIG. 1). The present invention can be applied.

1 Resin material 2 Foam molded product (resin molded product)
3 Bottom face part 4 Standing wall part 4A Upstream part 4B Downstream part 5 Rib 10 Mold 11 Fixed mold 12 Movable mold 14 Cavity 15 Gate tA, tB Thickness tC Base width of rib

Claims (5)

Applying a mold comprising a fixed mold and a movable mold movable relative to the fixed mold, assembling both molds to form a cavity communicating with the gate between the fixed mold and the movable mold, Filling this cavity with a resin material to which a foaming agent has been added from the gate in a molten state, and then allowing the movable mold to core back a predetermined amount with respect to the fixed mold,
At least a vertical molding portion in a region located substantially perpendicular to the core back direction, where the thickness increases largely due to the core back, and a region located substantially parallel to the core back direction, where the thickness increase is also small due to the core back. A parallel molded portion standing upright from the vertical molded portion in a substantially right angle direction, and a core back provided along the wall surface of the parallel molded portion at a predetermined distance from the gate of the parallel molded portion. And a rib for reinforcement substantially parallel to the core back direction with little increase in thickness,
In a molding method of a resin molded product for molding a resin molded product having
The parallel extending said gate communicating with the cavity, the thickness of the upstream portion in the parallel shaped portion between the rib provided along said parallel shaping section, in the direction opposite to the gate from the rib Make it thinner than the thickness of the downstream part in the molding part ,
With respect to the molten resin material injected from the gate into the cavity, in the region of the thin upstream portion, foaming is suppressed by suppressing a rapid drop in injection pressure, and the rib is opposite to the gate. A method for molding a resin molded product, characterized in that foaming is promoted by increasing a pressure reduction rate of an injection pressure in a region of a thick downstream portion extending in a direction . In the resin molded product, the vertical molding portion in a region positioned perpendicular to the core back direction is a bottom surface portion, and stands in a substantially right angle direction from a peripheral edge of the vertical molding portion in a region positioned parallel to the core back direction. The method for molding a resin molded product according to claim 1 , wherein the parallel molded portion provided is a box-shaped resin molded product having a standing wall portion . The resin molded article to be molded within the cavity, or claim 1, characterized in that the thickness of the upstream portion of the resin molded article or the upright wall is set to be equal to or greater than the base width of the rib 3. A method for molding a resin molded product according to 2. The resin molded article to be molded within the cavity, that the difference of thickness between the downstream portion of the upstream portion of the resin molded article or the upright wall is set above 0.5mm The method for molding a resin molded product according to any one of claims 1 to 3. The resin molded article to be molded within the cavity, according to claim 1, wherein the thickness of said upstream portion of the resin molded article or the upright wall is set to 1.5mm or less The molding method of the resin molded product of any one of Claims 1.